Creating face on subdivided edge distorted in top orthographic mode
This is because faces are not meant to be bent. All polygonal faces are secretly changed into triangles in the rendering engine, so if they are bent, it will split them arbitrarily. Create multiple faces one at a time, working your way around that corner. Select three or more vertices, and even if an edge to make them a face is missing, it will be auto-created.
Also, the top and bottom pre-existing faces seem to have mismatching edges round the corner, as in they are not exact copies of each-other and the differences seem random.